Wireless aerial system



Aug- 1939 K. H. BARUBOUR 2,168,857

WIRELESS -AERIAL S YSTEM Filed 19:57

INVENTOR K. H BARBQ TTORN EY Patented Aug. 8, 1939 {UNITED STATES PATENTOFFICE WIRELESS AERIAL SYSTEM Application February 27, 1937, Serial No.128,067 In Great Britain March 4, 1936 7 Claims.

The present invention relates to wireless aerial systems and hasparticular but not exclusive reference to receiving aerial systemscapable of operating over a wide band of wavelengths.

In the case of broadcast receivers, it is usual to employ a singleaerial which is tuned by inductance and capacitive elements containedwithin a receiver, the wavelengths employed for broadcast purposes beingsuch that no critical dimensions are necessary for the aerial itself.With the increase in the number of transmitting systems covering anextremely wide range of frequencies from very short waves such as areused in television systems, to the long waves employed by some broadcasttransmitters, it has become desirable from the point of view of emciencyto provide aerial systems which are de signed to operate over selectedwavelength ranges.

The object of the present invention is to provide an aerial system whichis capable of efficient operation over an extremely wide range ofwavelengths.

According to the present invention, a wireless aerial system comprises afirst aerial designed for operation over a band of relatively longwavelengths, and coupled by a transformer to a feeder, and a secondaerial designed to operate at a relatively short wavelength andconnected directly to said feeder. The first aerial may also be capableof operating at relatively short wavelengths, and for this purpose isgiven a length which is an integral number of quarter wavelengths at thefrequencies of the relatively short wavelengths at which it is intendedto operate. For the purpose of operation at such relatively shortwavelengths, the first aerial is connected to the feeder through afilter network which effectively short circuits the couplingtransformer. A further aerial designed for operation at wavelengths ofthe order used in television systems may be connected directly to thefeeder.

The first and second aerials are preferably arranged in a substantiallystraight line, the adjacent ends of these aerials being attached to asuitable insulator with which is associated the transformer and filterand to which there is connected one end of the feeder, the other end ofthe feeder being associated with one or more wireless receivingcircuits. The filter may be a high pass filter, or it may for example bean acceptor circuit tuned to a desired frequency.

More than one aerial may be connected directly to the feeder so that theefficient reception over several short wave bands may be obtained.

In order that the invention may be more clearly understood and readilycarried into effect, a wireless aerial system designed in accordancetherewith will now be described by way of example with reference to theaccompanying drawmg.

Referring to the drawing, a feeder l serves to couple an aerial systemincluding aerials 2, 3 and 4 to receiving apparatus '5 and is of thelowloss concentric type having a low characteristic impedance forexample of about 80 ohms. The upper end of the feeder is attached to ahollow Water-proof insulator 6 which is arranged to house transformerand filter elements I, 8, 9 and ill, and may be of the type shown in thespecification of British Patent No. 444,49 l. The aerial 2 is a footlength of wire and the aerial 3 a 39 foot length of wire. The adjacentends of the aerials 2 and 3 are attached to the insulator 6 and theremote ends are supported by insulators ll, i2, which are suitablysuspended from two elevated points such as for example, a mast or achimney. The two aerials thus form parts of a single suspension betweenthe two elevated points.

In the case of a broadcast aerial couple to a receiver through ascreened down lead, it is necessary to employ a transformer for couplingthe aerial 2 which has a relatively high reactive impedance to the lowimpedance feeder. A transformer l, 8 is therefore employed to couple theaerial 2 to the low impedance feeder i. One end of the primary winding 1of the transformer is connected to the aerial and one end of thesecondary winding 8 is connected to the centre conductor l3 of thefeeder i. The other ends of both windings l and 8 are connected to thesheath of the feeder.

It is known in practice that an aerial which is a small odd number ofquarter-wavelengths long has an impedance of between 40 and 100 ohmsbetween its end and earth. It is thus suitable for direct connection tothe ohm feeder. The 60 ft. aerial 2 which is a three-quarter wavelengthaerial at about 30 metres is therefore connected effectively directly tothe low impedance feeder l at this wavelength through a filter 9, i0having a low impedance at this wavelength and a high impedance atbroadcast wavelengths. The filter may be of the high-pass type having acut-off at a frequency somewhat below 10 megacycles per second (30metres) or it may be a series resonant circuit tuned to a frequency ofabout 10 megacycles per second. In the case of the series resonantcircuit shown comprising the condenser 9 in series with the inductanceIt the capacity of the condenser is preferably not greater than 0.0001microfarad in order that the efficiency for the shorter waves of thebroadcast waveband shall not be unduly impaired. By suitable choice ofthe value of the condenser 9, it can be arranged that the aerial hassubstantially greater efiiciency over the broadcast wavebands than wouldbe obtained if a plain unscreened down-lead were employed. In an exampleit has been found that the use of a condenser of 0.0001 microfarad givesan improvement of efficiency of about 10 decibels over the greater partof medium and long waves as compared with an open aerial. As mentionedpreviously, the filter is preferably enclosed in the insulator togetherwith the transformer l, 8.

The 39 foot aerial 3 operates as a quarter wavelength aerial at about 48metres and as a threequarter wavelength aerial at 17 metres. At otherfrequencies neither of the aerials 2 or 3 are well matched to the feederbut together they give a reasonably uniform input to the feeder atwavelengths between about 16 and 50 metres.

In order that the aerial system may operate satisfactorily at stillshorter wavelengths, for example for the reception of television signalson a carrier of frequency 45 megacycles per second, the third aerial 4is connected directly to the feeder. This aerial comprises a quarterwavelength conductor attached to the insulator 6, and is allowed to hangvertically. The lower end is connected to an insulator M which issuitably anchored. For a frequency of 45 megacycles per second theaerial conductor 4 should have a length of about 5 feet. This aerial maybe converted into a half wave dipole fed at its centre by connecting aconductor not shown in the drawing, to the sheath of the feeder l thisconductor having the same length as the conductor which extendsvertically downwards and being supported so that it extends verticallyupwards from the feeder.

Signals at wavelengths of the order of '7 metres are received almostexclusively by the direct ground ray which is generally verticallypolarised. A vertical aerial as described above is therefore the mosteffective. Signals received on somewhat longer wavelengths are oftenreceived from very great distances and they have then been subjected toreflection, bending and scattering in the ionosphere. The angle ofpolarisation is therefore very variable and it is more ad vantageous toconsider the physical layout of the system than to take account of thedirection of polarisation of the signals to be received although ofcourse if necessary this can be done.

If space is limited, the 60 ft. aerial 2 may be replaced by a 20 ft.aerial which will operate as a quarter wavelength aerial at 30 metres,but this reduces the effective pick-up on broadcast wavelengths. Theconnections remain exactly as shown in the drawing.

At the receiver end of the feeder the central conductor 13 is connectedto the movable contact of one of two ganged switches I5 and I6, and thesheath I is earthed. A conducting lead is taken from the moving contactof switch Hi to the aerial terminal A of the receiver. For reception ofwavelengths below approximately 30 metres, the moving contacts areplaced in the uppermost position, and the central conductor 13 is thenconnected directly to the aerial terminal A. When the moving contactsare in the mid-position a step-up transformer I! suitable for receptionin the range of wavelengths between 30 to 200 metres couples the feederto the terminal A. In the lower-most position of the moving contacts asecond transformer I8 couples the feeder to the terminal A for receptionin the range of wavelengths between 200 and 2,000 metres.

The two switches l5 and I6, together with the transformers l1 and [8 maybe housed separately or may be built in the receiver itself.Alternatively the receiver can be built so as to offer suitable inputconditions in order that it will operate without the matchingtransformers I1 and I8. This would be done for example, by providingsuitable tappings on the input coils.

The concentric type of feeder as described and shown serves to minimisethe pickup of local interference on all the wave bands on which signalsare to be received.

By suitably modifying the lengths of the two horizontal aerials 2 and 3,they may be arranged to aid reception at the frequency of the televisioncarrier. For example, the horizontal aerials may give increasedreception at the higher television sideband frequencies, therebyeffectively flattening the response curve of the system at thetelevision carrier frequency. In the particular arrangement describedthe 60 foot aerial 2 is effectively three wavelengths and the 39 footaerial is effectively two wavelengths of the television signals. In thiscase each presents an impedance of about 2000 ohms to the line and, dueto the degree of mis-match, television signals from these aerials arevery inefficiently fed to the receiving circuits.

In the above description the shortest wave signals to be received havebeen called television signals. It will be understood of course that theaerial can be used for the reception of signals other than televisionsignals, and again the lengths of the various aerial elements can bemodified according to the frequencies or hands of frequencies which itis desired to receive. More than three aerials may be included in thesystem depending upon the number of separate wavelengths at which thesystem is desired to operate.

The aerial can also be used for simultaneous reception of two or moresignals of different wavelengths, filter circuits being provided toseparate out the different frequencies for transmission to the desiredcircuits. While use of the aerial has been described in connection withreception, the system may also be used for transmission purposes.

It will be realised that a balanced system can be used comprising a twowire balanced feeder. It will then be necessary to use a balanced aerialsystem, that is to say, a further set of conductors will be provided,corresponding conductors forming at the short wavelengths, the twohalves of a half wavelength dipole.

I claim:

1. A wireless aerial system designed for operation over a band ofrelatively long wavelengths and also at a relatively short wavelengthcomprising in combination an aerial, a transformer for coupling saidaerial to a feeder for the purpose of long wave operation and means forcoupling said aerial directly to said feeder for operation at awavelength at which said aerial is substantially an odd number ofquarter wavelengths long, said means comprising a series tuned circuitresonant at the resonant frequency of said aerial, said aerial beingconnected to said feeder through the series tuned circuit, saidtransformer being effectively short-circuited by the series tunedcircuit.

2. A wireless aerial system comprising a transmission line including aninner conductor and an outer conductor, a first aerial for operatingover a band of relatively long wavelengths such as the broadcast range,said first aerial having a length which is equal to an integral numberof quarter wavelengths at the frequency of a first relatively shortwavelength desired to be received through said aerial system, atransformer for coupling said first aerial to said transmission line, asecond aerial directly connected to the inner conductor of saidtransmission line for operation at a second relatively short wavelength,and means including a filter network which effectively shortcircuitssaid transformer at said first named short wavelength for directlyconnecting said first aerial to said inner conductor.

3. A wireless aerial system according to claim 2 wherein there isprovided a hollow insulator, said transformer and said filter beinghoused within said hollow insulator and the adjacent ends of said firstand second aerials are supported by said hollow insulator.

4. A wireless aerial system according to claim 1 wherein there areprovided two additional aerials designed for operation at wavelengthsdifferent from that of said long wave aerial and means directlyconnecting said two additional aerials to said feeder.

5. A wireless aerial system according to claim 1 where there is provideda first additional aerial designed for operation at a wavelength whichis short compared with the operating wavelength of said long wave aerialand a second additional aerial designed for operation at a wavelength ofthe order used in television systems and means directly connecting saidfirst and second additional aerials to said feeder.

6. An aerial system comprising a first aerial adapted for operation overa band of relatively long wavelengths, a feeder line, means comprising atransformer for coupling said first aerial to the feeder line, a secondaerial adapted for operation at a relatively short wavelength, saidsecond aerial being directly connected to the feeder line and means foradapting the first aerial for operation at relatively short-wavelengthscomprising a filter network connected directly between the first aerialand the feeder line, and arranged so as to effectively short-circuitsaid transformer.

7. An aerial system comprising a pair of antenna wires of differentlengths, means comprising an insulation element for connecting one endof one of said wires to one end of the other of said wires, the remoteends being adapted to be insulatingly suspended from two spaced elevatedpoints so that said two wires form a single suspension between the twopoints, a low loss concentric type feed line, a transformer for couplingthe longer of said antenna wires to one end of said feed line, saidtransformer being effective throughout a range of relatively lowfrequencies, a filter device adapted to pass a range of frequencieswhich is relatively high as compared to the range of frequencies forwhich said transformer is effective .of the high-pass type connecteddirectly between said longer antenna wire and the inner conductor of thefeed line, said inner conductor being also directly connected to saidother antenna wire.

KENNETH HEYWARD BARBOUR.

